<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <input type="text"> <button>点击</button>
  <div></div>
  <script>
    //trim 方法去除字符串两侧空格
    var str = '   andy    ';
    console.log(str);
    var str1 = str.trim();
    console.log(str1);
    var input = document.querySelector('input');
    var btn = document.querySelector('button');
    var div = document.querySelector('div');
    btn.onclick = function(){
      var str = input.value.trim();
      if(str === ''){
        alert('请输入内容')
      } else {
        console.log(str);
        div.innerHTML = str;
      }
    }
  </script>
</body>
</html>